Seeing this footage, and just how fast is spread is scary. I would use an artificial tree, and make sure you have a smoke detector (they are only around 10$)
in the same room, or very close to it as the tree is.

This is some of the scariest footage I've ever seen, but you can probably tell that from the GIF. Fire spreads up the tree and gushes across the ceiling, setting the rest of the room ablaze. Smoke engulfs the frame from the top down until all is black. It's a real eye-opener as to the dangers of a short in a string of Christmas lights.

Unfortunately, the quality of this digital copy leaves much to be desired. The timer is a nice touch, but I could do without it. The codec used here causes the image to be very pixilated and undermines the directness of the film's message.

But it's a small enough file that you should download it anyway. Another worthy addition to a catalog of films for closet pyros.